Conventional portable audio systems often include a headphone that is connected to a media player (e.g., by one or more wires or by wireless technology). Conventional headphones may include one or two speaker assemblies having an audio driver that produces audible sound waves with a diaphragm. For example, FIGS. 1 and 2 illustrate speaker assemblies 100 and 200, respectively, for a conventional headphone.
Referring to FIG. 1, the speaker assembly 100 may include a diaphragm 110 connected to a rim of a support structure 120, which may cause the outer edge of the diaphragm to be relatively rigid. In the center area of the diaphragm 110 is a rigid cone member coupled to a magnetic member (e.g., coil, magnet). The portion of the diaphragm 110 outside of the rigid cone member may include a suspension member that determines the stiffness of the diaphragm 110 that permits the magnetic member attached to the diaphragm 110 to move back and forth in a magnetic field responsive to an audio signal. As a result, the diaphragm 110 generates audible sound waves in the air proximate the speaker assembly 100 that correspond to the frequencies of the audio signals.
Conventionally, the diaphragm 110 includes a single suspension member coupled between two rigid members (e.g., the rim of the support structure 120 and the cone member). As a result, the speaker assembly 100 acts as a single mass/spring system having a single resonant frequency that is at least partially dependent on the mass of the rigid cone member and the spring constant of the flexible suspension member of the diaphragm 110. For example, some diaphragms may have a resonant frequency of approximately 90 Hz. The resonant frequency in such a configuration may be decreased by increasing the diameter of the diaphragm 110 and/or by reducing the thickness of the plastic material. It may, however, be difficult or impractical to form a diaphragm 110 having a conventional design that exhibits a lower resonant frequency, because the size of the diaphragm 110 would be too large, and/or the diaphragm 110 would be too thin and susceptible to damage.
Referring to FIG. 2, in additional previously known speaker systems, a speaker assembly 200 may include a metal suspension member 210 (instead of a plastic diaphragm) connected to a rim of a support structure 220. The suspension member 210 may be generally circular, and may have flexible beams connecting a radially outer rigid portion and a radially inner rigid portion. The inner rigid portion may be a platform to which a coil and a magnet may be attached. The speaker assembly 200 of FIG. 2 may also include a single suspension member 210 coupled between two rigid members (e.g., the rim of the support structure 220 and the cone member).
Speaker assemblies may also include tactile bass vibrators that are configured to generate tactile vibrations within the speaker assemblies that may be felt by the user. Tactile bass vibrators may also at least partially supplement the acoustic bass frequencies of the speaker assembly. Conventional tactile bass vibrators may include a single suspension member coupled between two rigid members, which result in a resonant frequency that is tuned to a desired bass frequency to achieve the desired effect; however, conventional tactile vibrators typically have a limited optimal frequency range of vibration amplitude (i.e., bass frequencies only).